Lightweight, low cost printed wiring board panels used in planar or conformal phased array avionic applications, high speed digital boards, and power distribution boards, for example, require easy interconnect, continuous ground planes and optimized thermal and structural performance. Manufacturing very large surface area boards associated with phased array antenna arrays provides several challenges. For example, the radio frequency, control and power signals must be distributed over a large area. Array or other different self-supporting panels must provide low weight per unit area and be manufactured and assembled in an efficient manner without undue interconnect complexity.
Some prior art printed wiring boards are formed as circuit card assemblies (CCA) and include dedicated structural panels required to support the electronics. Manual labor often is required for assembling these panels and electronics, typically using screws or similar fasteners. Ground springs are also often required for grounding support. Because discrete radio frequency (RF), power and control signals must be distributed (or routed) throughout the board, these multiple circuit card assemblies require specialized assembly processes. Extensive interconnects integrate different boards, often requiring a high parts count, adding to the documentation, procurement and logistic difficulties associated with the development, manufacture and sale of such boards. Antenna elements and feed networks also require complex grounding. These boards overall only have a modest weight efficiency.
There have been some proposals to provide a lightweight, low cost integrated and distributed circuit card assembly. Some of these approaches still maintain a low structural integrity, however. These proposals often produce circuit card assemblies having limited environmental robustness and mandate a larger number of mounting points per card to secure the card to a housing or other support structure. These proposals also have a low weight efficiency and use surface mounted discrete components and radio frequency (RF) “modules.”
Some current circuit card assembly fabrication techniques attach the board to heat sinks or housings, via fasteners or adhesive bond lines. For example, some metallic heat sinks are laminated to printed wiring boards, but this assembly process does not provide intimate electrical contact even if accomplished with electrically conductive adhesives. Some conductive adhesives have a low shear efficiency and yield assemblies with poor stiffness and strength. Some printed wiring boards have copper metallic layers, but these layers have contributed little to the printed wiring board structure because of their limited thickness and low specific stiffness in design. Other boards have poor coefficient of thermal expansion (CTE) with devices and/or other board materials forming the overall circuit card assembly.